**Understanding Punctuation in Relative and Subordinate Clauses**

In the realm of grammar, understanding the correct use of punctuation in various sentence structures is crucial for clarity and precision in written communication. One area that often causes confusion is the appropriate use of commas in relative and subordinate clauses. These clauses, integral to providing additional information about a noun or a broader idea, come in two main types: restrictive (or essential) and nonrestrictive (or nonessential) clauses. The punctuation rules governing these clauses play a significant role in determining the flow and readability of sentences.

### Definition of Relative and Subordinate Clauses

**Relative Clauses**  
A relative clause is a type of dependent clause that modifies a noun or pronoun. It usually begins with a relative pronoun (such as who, whom, whose, which, or that) or a relative adverb (like when, where, or why). Relative clauses provide essential or additional information about the noun, depending on whether they are restrictive or nonrestrictive.

**Subordinate Clauses**  
A subordinate clause, also known as a dependent clause, adds information to the main clause and cannot stand alone as a complete sentence. It often starts with subordinating conjunctions such as although, because, since, unless, or while. These clauses can function as adverbial, adjectival, or nominal clauses in a sentence.

### Punctuation Rules for Relative and Subordinate Clauses

**Restrictive Clauses**  
Restrictive clauses, also known as essential clauses, provide information that is crucial to the meaning of the sentence. This type of clause narrows down the identity of a noun or pronoun and is integral to the sentence’s meaning. For example, in the sentence "The book that has a red cover is mine," the clause "that has a red cover" is restrictive as it specifies which book is being referred to. Importantly, restrictive clauses should not be separated by commas. Omitting commas indicates that the information provided by the clause cannot be removed without changing the fundamental meaning of the sentence.

**Nonrestrictive Clauses**  
Nonrestrictive clauses, on the other hand, offer extra information about a noun that is already sufficiently identified. The information provided by nonrestrictive clauses can be considered additional rather than essential. For instance, in the sentence "My bicycle, which has a bent frame, is old," the clause "which has a bent frame" is nonrestrictive; the identity of the bicycle is clear without it, and the information is merely descriptive. Nonrestrictive clauses must always be enclosed with commas, signaling that the information could be omitted without altering the sentence’s primary meaning.

### Examples and Explanation

To further explicate these rules, consider these examples:

1. "Students who study hard excel in exams." (Restrictive)
   - The clause "who study hard" specifies a particular group of students, hence no commas are used.

2. "My brother, who lives in New York, is visiting us next week." (Nonrestrictive)
   - The clause "who lives in New York" provides extra information about "my brother" whose identity is already clear, thus it is enclosed in commas.

### Importance of Correct Punctuation

Correct punctuation in relative and subordinate clauses is not merely a matter of grammatical correctness but also pivotal in avoiding potential ambiguity. Misplacing commas can lead to misunderstandings about which part of the sentence is being modified or emphasized. For instance, missing commas in a nonrestrictive clause could mislead the reader to assume that the clause is essential to the subject’s identity, thereby altering the intended meaning.

In summary, the distinction between restrictive and nonrestrictive clauses and their respective punctuation with commas are fundamental in English syntax. This dichotomy enhances the clarity and precision of language use, ensuring that readers understand exactly what the writer intends to convey. Thus, mastery of these punctuation rules is essential for anyone looking to excel in written communication.